The present invention relates to a condrapable hydrophobic nonwoven web of continuous fibers and a method of making the same; and more particularly to a method of making the same using a fiber surface-modifying agent.
Nonwoven webs of continuous fibers are well-known in the fabric art and are commonly known as xe2x80x9cmeltspuns,xe2x80x9d a term derived from the primary members of the classxe2x80x94namely, meltblowns, spunbonds and combinations thereof. While other nonwoven webs are known in the art, they contain staple fibers (that is, short fibers rather than continuous fibers), carded webs being a well-known example of such nonwoven webs of non-continuous fibers.
The meltspun webs have utility in a wide variety of different applications. Some of these applicationsxe2x80x94for example, use as diaper back sheets and cuffsxe2x80x94arise out of the hydrophobic nature and barrier properties of the meltspun web due to the nature of the material used in the web. For example, a web formed of polypropylene fibers typically exhibits the high degree of hydrophobicity required for use in diaper back sheets and cuffs, surgical gowns and the like where water absorption by the fabric formed from the continuous fibers would be undesirable, but exhibits an inferior hand and drape. On the other hand, meltspun webs formed of other materials, such as polyethylene and polyethylene/polypropylene copolymers, either exhibit an unsatisfactorily lower level of hydrophobicity for particular applications or are even hydrophilic in nature, but exhibit superior relative softness and drape. In this instance, the materials may be rendered hydrophobic or more hydrophobic by the use of a hydrophobic material such as polydimethylsiloxane (hereinafter xe2x80x9cPDMSxe2x80x9d). The PDMS may either be incorporated into the polymer mix from which the fibers are made or applied to the web after web formation.
An economic application of particular web additives to a web is typically achieved by dispersing the additive in an aqueous medium so that the additive-containing aqueous medium may thereafter be conveniently sprayed, coated, or otherwise applied to the web, with the aqueous medium thereafter being removed from the web by simple drying in order to leave the additive on the fiber surfaces of the web. Some of these additives are hydrophilic in nature and thus easily dispersed in the aqueous medium. Others are hydrophobic and thus require the use of a hydrophilic emulsifier (such as long chain fatty acids) in order to disperse the additive in the aqueous medium. In the latter instance, removal of the aqueous medium leaves not only the desired additive on the fibers, but also the hydrophilic emulsifier so that the treated web is either hydrophilic or at least less hydrophobic than it would have been prior to treatment with the additive. Exemplary of the additives are the surfactants and lubricants commonly used to enhance the aesthetic tactile properties, such as softness, smoothness and feel. Use of a surfactant to provide softening of the web lessens the hydrophobic nature of the web and, indeed, often produces a hydrophilic product unacceptable for particular applications requiring a hydrophobic nature. See, for example, U.S. Pat. No. 3,973,068.
Speaking more particularly, it is known to provide a hydrophobic nonwoven web of continuous fibers formed of polypropylene. It is known to apply to the fibers of such a web, as a softener or lubricant, a hydrophilic additive dispersed in an aqueous medium (to facilitate economical application of the additive onto the web) and then to dry the web to remove the aqueous medium and leave a treated web. However, the treated web thus produced is typically no longer sufficiently hydrophobic for its intended use either because the additive with which it was treated is itself primarily hydrophilic or because a quantity of hydrophilic emulsifier was used to disperse a non-hydrophilic additive in the aqueous medium.
Accordingly, it is an object of the present invention to provide a method of making a condrapable hydrophobic nonwoven web of continuous fibers.
Another object is to provide such a method using as an additive a fiber surface-modifying agent dispersed in an aqueous medium where the web retains its essentially hydrophobic nature.
A further object is to provide such a method wherein the agent is dispersed in the aqueous medium using a hydrophilic emulsifier in a quantity such that it does not adversely affect the hydrophobic nature of the web.
It is also an object of the present invention to provide products made by the method.
It has now been found that the above and related objects of the present invention are obtained in a method of making a condrapable hydrophobic nonwoven web of continuous fibers having an initial condrapability, comprising the steps of providing a hydrophobic nonwoven web of continuous fibers and applying to the web a fiber surface-modifying agent dispersed in an aqueous medium. Finally, the web is dried to remove the aqueous medium and leave a condrapable hydrophobic web. In one aspect of the invention, the agent essentially comprises an amino-modified polydimethylsiloxane. In another aspect of the invention, the dried web is characterized by a substantial hydrophobicity, as measured by a strike-through of over 300 seconds, and by a substantial improvement in condrapability, as measured by a Handle-O-Meter decrease (in the force measured) of at least 15% (and preferably at least 20%) average for MD and CD.
Preferably, the web is a meltspun nonwoven.
In a preferred embodiment, the amino-modification is the substitution of an aminoalkyl group for a methyl group of PDMS. Thus, the amino-modified PDMS is: 
where
independently Y, X=a termination group;
Rxe2x95x90R1xe2x80x94NHxe2x80x94R2;
R1=xe2x80x94(CH2)pxe2x80x94, where p=greater than zero;
R2=hydrogen, alkyl, cycloalkyl, aryl, aminoalkyl, alkylaminoalkyl, cycloalkylaminoalkyl, or aminoaryl; and
independently n, m=greater than zero.
Preferably,
Rxe2x95x90CH2xe2x80x94CH2xe2x80x94CH2xe2x80x94NHxe2x80x94R2
In a preferred amino-modified PDMS, the combined n+m is 400 to 1,500 (preferably about 1,100); the degree of amino modification is 2 to 5 (preferably about 3.5); and the amino number is 0.1 to 0.3 (preferably about 0.12-0.15). The molecular weight of the amino-modified PDMS, at the time of application to the web, is about 30,000 to 150,000 (preferably 70,000-100,000).
The wet pick-up of the web is 20 to 200% based on the dry web; the aqueous medium has 0.5 to 20% agent therein, based on the weight of the aqueous medium; and the dried web has 0.005 to 0.5% agent thereon, based on the weight of the dried web.
The fibers are selected from the group consisting of polyolefins, polyesters, polyamides, copolymers thereof and blends thereof. Preferably the fibers are polyolefins selected from the group consisting of polyethylene, polypropylene, copolymers thereof and blends thereof. Optimally, the fibers are polypropylene. The fibers are consolidated by a process selected from the group consisting of thermal bonding (fusion bonding), chemical bonding (resin bonding), hydroentanglement and needle punch, preferably by a thermal bonding process.
The agent may be dispersed in the aqueous medium by at least one hydrophilic emulsifier. Preferably the hydrophilic emulsifier is nonionic, and optimally it is at least one ethoxylated fatty alcohol. The hydrophilic emulsifier has an HLB of 8 to 17 and is present at 3 to 30%, based on the weight of the agent. The hydrophilic emulsifier may include a nonionic or cationic co-emulsifier.
The present invention also encompasses a condrapable hydrophobic nonwoven web of continuous fibers, comprising a hydrophobic nonwoven web of continuous fibers, and a fiber surface-modifying agent on the web to form therewith a condrapable hydrophobic web. The agent essentially comprises an amino-modified polydimethylsiloxane, and the condrapable hydrophobic web is characterized by a substantial hydrophobicity, as measured by a strike-through over 180 seconds, and by a substantial improvement in condrapability, as measured by a Handle-O-Meter decrease of at least 15% average for MD and CD relative to the initial condrapability.